Recovery of relief material



Nov. 1-, 1932. w. H. KENETY 1,885,918

RECOVERY OF RELIEF MATERIAL Filed Jan. 17, 1931 Patented Nov. 1, 1932 UNITED STATES PATENT OFFICE WILLIAM H. KENETY, OF CLOQ UET, MINNESOTA, ASSIGNOR TO CHEMIPULP PROCESS INC., 013 WATER'IOWN, NEW YORK, A CORPORATION OF NEW YORK RECOVERY OF BELIEF MATERIAL Application filed January 1'}, 1931. Serial No. 509,299.

The present invention relates to processes for cooking wood and other cellulosic material for the formation of pulp, and it has particular reference to the preliminary op- 5 erations in the sulphite process, to the relief of the digester,lto the utilization of the heat in the materials relieved, to the recovery of the materials, and to the combination of such utilization and recovery with said preliminary operations.

In the cooking of wood by the sulphite process, using any of the suitable bases, of which calcium, magnesium and sodium are commonly known, it is necessary to use an acid sulphite and an excess of free sulphurous acid dissolved in the cooking liquor. The excess acid usually varies in amount. It is not constant, because it held very loosely in the liquor, and increased heat and de- 29 creased pressure both cause it to be discharged from solution in the liquor. It is therefore customary to charge a digester with a cooking li nor in which the free acid content is very hlgh. The tendency of the subsequent heating to drive it off is somewhat balancedby the tendency of the increasing pressure to prevent its escape. In the present practice of the sulphite process .where steam is injected into the liquor there 9 is an escape of much free acid from the process, and this is accompanied by discharge of a uantity of the cooking liquor. Vents or relief lines suitably placed about the digester have valved controls to regulate the escape of such material and to control the pressure.

It is quite desirable to have all the chips in the digester covered with the cooking liquor, and accordingly the digester is quite full. The injection of the heating steam causes condensation, and in order to accommodate the increased volume of water resulting from such condensation a portion of the liquor is released. It is customary to bleed liquor from the digester at a rate which will compensate for the water being added. This liquor and the acid which is also set tree are greatest in amount at the beginning of the heating operation and in the early part of the cook, but nevertheless a substantial amount of gas and vapor escape during the entire cook. The material first removed by relief is of greater purity than that which is later relieved, for after the cooking has proceeded there are present in the liquor various impurities'removed from the chips, such as pitch, lignins, dissolved resins, oils, organic acids, etc.

In the preliminary operations of the sulphite process the liquor is usually introduced so that heating begins at a temperature of about 70 (1, and cooking action does not begin until three or four hours after the heating commences. This heating period involves the introduction of much water as steam, and requires the displacement of an equivalent amount of liquor, with the disadvantage that the original liquor is diluted. Much of the cooking value in the liquor, both as dissolved solids and as free acid, is thus lost through the relief system before any cooking takes place, and the loss continues as cooking occurs. Much heat is carried away from the digester during the relief.

Various processes have been proposed for conserving the chemical value and the heat of the relieved materials, such, for example, as the introduction of them into liquor being prepared fora subsequent cooking operation. Absorption of the free acid gas at atmospheric and at greater pressures has been proposed, but there are disadvantages to these operations. At atmospheric pressure the temperature which can be attained is limited. At higher pressures the back pressure increases and a constant and uniform relief cannot be maintained. Furthermore, the introduction of the relief materials into the new liquors contaminates them with the impurities which they carry, and there is thus an accumulation of detrimental materials which gives low grade pul in subsequent cooking operations with suc liquor.

In a copendin joint a plication of the a plicant with W. Stevens, Serial 0. 249,845, filed January 27, 1928, there is described an accumulator system of which the present invention is an extension and an improvement. In the prior application there is shown an accumulator containing a heat exchanger. The relief. pipe from the digester is divided into two'branches, one of which is connected to the heat exchanger and the other of which enters the accumulator for discharging relief material into the accumulator.

One object of the invention is the preparation ofthe cooking liquor, including reheating thereof by relief material and enrlchment thereof by relief material.

Another object of the present invention is the provision of automatically controlled means for distributing the flow between said two branches.

Still another object of the invention is the provision of automatically controlled means for regulating the diversion of relief material of a digester from discharge into an accumulator to other means of disposal.

Still another object of the invention is the automatic control of the pressure of a digester by automatic control of the flow of relief material.

Still'another object of the present invention is the provision of two accumulators, and the re ulationand distribution of relief material tween the contents of the two accumulators.

Various other and ancillary objects and advanta s of the invention will become apparent tom the following description and explanation of an exemplary embodiment of the apparatus of the invention which appears in the accompanying drawing.

In the drawing there is shown a digester and two accumulators with suitable pipe connections between them.

It is to be understood that the invention is not limited to the particular arrangement, relation and combination of parts which are shown in the drawin Various other forms are contemplated. or example, several digesters may beoperated in connection with the two accumulators by providing a common or separate heat exchanger for each digester in one or both of the accumulators, employing the invention described in a copendin 'omt application of the applicant and J.

ggxens, Serial No. 508,911, filed January 15, 1

In the drawing a digester 10 is provided at the bottom with a valved blow lme 11, a steam line 12 for su plying heat by steam injection, and a f line 13 for cooking liquor. At the top of the digester there is a relief line 14, generally for gas relief, and at the side thereis a liquid relief line 15. These lines are preferably joined forming a line 16 for conveying as and liquid, here1nafter referred to as re 'ef material, fromthe digester, according to well known ractice. Separating devices may be inserte in the line1i7f desired, as indicated diagrammatically at Two accumulators are provided, each suflicient in size to hold about one and one-half times as much liquor as is required to char e a digester for cooking. Raw liquor may fed to one accumulator, wherein it is enriched and heated by direct discharge, and heated by transfer methods from a heat exchanger. The relief material from the heat exchanger may be either discharged into the second accumulator, or passed through a heat exchanger therein. Liquor may be transferred from one accumulator to another as desired, and it preferably passes from a supply of raw liquor to one accumulator thence into the second accumulator, and thence into the di ester. Y

he arrangement is preferably such that one accumulator is elevated with reference to the other and to the digester, and such that the liquor receives its last heating and enriching under a hydrostatic head from the liquor in the elevated accumulator.

In the drawing raw liquor from a supply 20 may be forced by pump 21, through the pipe connection 22 into an elevated accumulator 23. Relief line 16 enters the accumulator for dischar e therein at 24. A valve 25 is shown in t e discharge line. A heat exchanger 26, such as a coil of pipes, is connected through a valved line 27 to the relief line 16. A pressure operated valve, such as a pop valve 28, which can be set and adjusted for any predetermined pressure, is arran ed to open a passage in line 27, to permit re ief naterial to flow through the heat exchanger 2 The heat exchanger 26 is connected by pipe line 29 to a Y-connector 30 from which one branch 31 enters a lower accumulator 32 for discharge thereinto. A second branch 33 passes through second pressure controlled valve 34 into a heat exchanger 35 in accumulator 32. A waste line 36 connects the heat exchanger 35 with a waste outlet or some other recovery system. The top of the accumulator 32 connects by pipe 37 with the feed pipe 13 to digester 10. The bottom of accumulator connects by pipe 38 with the bottom of the elevated accumulator 23. A valved connection 39 may exist between pipes 37-13 and 38 in the particular arrangement illustrated in' order to give flexibility in use of the system,permitting one accumulator to be cut 'out. Under such a condition the apparatus will conform to and may be operated according to the description found in the copending application Serial For the above purpose of flexibility, the

raw liquor feed pipe 22 is connected to the pipe line 38, and suitable valves as shown are placed in the connections.

A particular advantage of the two accumulators, and especially of one above the other, is the fact that a higher heat and a greater pressure may be obtained, thus insuring greater saturation with gas. When the upper accumulator 23 is freshly filled'with raw and cooler liquor, the lower accumulator has the enriched and hotter liquor which is to be further enriched and heated. At this stage it may frequently be desirable to convey relief directly to the lower accumulator, either into it or through the heat exchanger, for the reason that passage through the heat exchanger 26, which is surrounded with much cooler liquid, may eilect cooling of the relief material to such a point that the relief in line 29 would cool the heated contents of the lower accumulator. I therefore provide an arrangement for preventing such a condition until the liquid content of the upper accumulator attains a temperature assuring a discharge in line 29 that is hotter than the liquid content of the lower accumulator. A by-pass line 41 controlled by valve 42 leads from pipe 16 to the pipe 29. By reason of this connection the digester may be made to relieve to either accumulator, or to both simultaneously. By controlling the settings of the pop valves the quantity of relief to the respective accumulators may be varied as well as the manner of utilizing the relief, whether for discharge or for heat transfer. The static head of the upper accumulator may be imposed on the liquid in the lower accumulator, and this pressure permits greator saturation of the liquid accumulator 32 with the sulphur dioxide. Ordinarily, the release of liquid from the bottom of an elevated accumulator into a digester causes the escape from the liquid of considerable gas. For example, when the char ed liquid in the u per accumulator is with rawn by means of pipe 38, the accumulator 23 becomesfilled with gas which is released from the liquid. If this liquid was carried to a digester it would be weaker therein than it was in the accumulator before withdrawal. The gas remaining in the accumulator is usually forced out through a venting valve 43 at the top when a new charge of liquor is forced in. However, the gas need not be lost as it may be conducted to other apparatus, but it is lost as an important part of the highly charged digestion liquor. I prefer to conduct it by pipeline 44 into the pipe line 29 so that the liquid fed into accumulator 23,

forces the gas out and back into the liquor in the lower accumulator where it originated. Using two accumulators, and forcing liquor .contaminated with impurities.

from the top of the lower. one, under the static head of the upper one, prevents such loss of gas in the transfer to the digester of the more highly saturated and heated liquor of accumulator 32. Accordingly the method of emptying the accumulator from the top by pressure from the bottom is an advantageous improvement over the method shown in the prior joint application of Stevens and the applicant Serial No. 249,845, above referred to.

In operation, raw liquor is supplied to the accumulators. A cooking process in digester 10 requires relief material to flow in line 16. Failure to permit flow causes an increase of pressure in the digester. In the beginning relief material may flow through discharge pipe 24 into the liquor in the elevated accumulator, thus enriching and heating it, building up a pressure therein. As the pressure approaches that in the digester, considering the static heads involved, the flow of relief material is reduced and may be stopped by the back pressure. This builds up the digester pressure to a set value of the pop valve 20 which opens and permits further relief through the heat exchanger. This relief through the pop valve may occur before orv after the flow in discharge line 24 has ceased because of back pressure. The variations of pressure and the working of the valve cooperate to make a practically constant digester pressure automatically.

The relief material from the heat exchanger 26 may be of high quality for relief material. By this is meant that the cooking process in digester 10 may not have progressed so that the relief material is highly It may be valuable to enrich liquor in accumulator 32. It may be discharged into the accumulator, or its heat may be utilized by passing it through the heat exchanger 35. op valve 34 may be set at a higher pressure than pop valve 28 because in addition to mechanical pressure there is the added head in connection 29. Pop valve 28 may be set to regulate the diversion of relief in accumulator 32.. Pop valve 34 may be set to operate at a time after pop valve 28 when digester pressure is higher, considering the static heads, so that a portion of the relief from line 29 may be discharged into accumulator 32.

When a digester is to be charged the valves may be opened and the contents of the elevated accumulator will force the contents of the lower accumulator into the digester, with no loss of gas, and with no remnant of gas'in the lower accumulator. The tendency of the highly charged liquid to release gas in the digester is offset by the cooling in the digester on contact with chips therein. Then the upper accumulator may be supplied with a new charge of liquor and the process re- It will be understood that various changes and modifications may be made in the appa= ratus without departure from the invention.

For example the liquor in the elevated accumulator may be run directly into the digester. Fresh liquor may be run through connections 22 and 38 into the lower accumulator, and its contents raised through connection 37 and an extra valved connection 40 between line 37 and the elevated. accumulator. In the event both accumulators are cut out, raw liquor may be fed directly to the digester 10 through lines 22, 38, 39, 37 and 13.

The invention provides apparatus which is highly flexible in use, which permits eflicient use of heat and waste relief material, and which forms a hot rich charging liquor, the use of which shortens the time of cooking and improves the economy of the process.

In the appended claims I aim to define all the improvements in the apparatus and the process. I do not intend to be limited by the description and drawing to the specific disclosure here given, but contemplate such other arrangements and changes as fall with in the scope of the claims.

I claim:

1. Apparatus for recovering relief material and the heat thereof from the bleeding of a heated pressure cooker which comprises a pressure digester, a pressure vessel for containing liquid to be heated, a discharge pipe entering said vessel, a heat exchanger in said vessel, 21 pipe connection from said discharge pipe to said di ester, a pipe connection from said heat exchanger to said digester, and a pressure operated valve in said last pipe con-- nection adapted to open and establish flow from said digester to said heat exchanger at a predetermined pressure on the digester side of said line.

2. Apparatus for recovering relief material from a pressure cooker comprising a pressure digester, an accumulator for holding liquid under pressure, a connection from the digester into the accumulator for discharge of relief material into the accumulator, a heat exchanger in the accumulator, a connection from the digester to the heat exchanger for the flow of relief material from the digester to the heat exchanger,a second accumulator,a connection from the heat exchanger into said second accumulator, a connection between the two accumulators for the transfer of liquor from one to another, means to supply raw liquor to one accumulator, and a connection from the other accumulator to the digester for filling the digester from said accumulator.

3. Apparatus for recovering relief material from a pressure cooker comprising a pressure digester, an accumulator for holding liquid under pressure, a connection from the digester into the accumulator for discharge of relief material into the accumulator, a heat exchanger in the accumulator, a connection from the digester to the heat exchanger for the flow of relief material from the digester to the heat exchanger, a second accumulator, a connection from the heat exchanger into said second accumulator, a heat exchanger in the second accumulator, a connection from the first heat exchanger to the second heat exchanger, a connection between the two aocumulators for the transfer of liquor from one to another, means to supply raw liquor to one accumulator, and a connection from the other accumulator to the digester for filling the digester from said accumulator.

4. An accumulator system for relief material from a pressure digester comprising in combination, a digester, two interconnected accumulators arranged for passage of li uor from one through the other to a digester a eat exchanger in each accumulator a discharge pipe entering each accumulator, a discharge outlet pipe entering each accumulator, valved connections from the digester for carrying source of relief material extending to the heat exchanger and to the discharge pipe of one accumulator, and valved connections from said last named heat exchanger to the second heat exchanger and the second discharge pipe.

5. An accumulator system for relief material from a pressure digester comprising in combination, a pressure digester, two accumulators, one being elevated above the other and above the digester, connections from the bottom of the accumulator higher to one end of the lower accumulator and from the other end of the lower accumulator to the digester, a bubbler pipe in each digester, a heat exchanger in each digester, valved connections for relief material extending from the digestor to the bubbler pipe and to the heat exchanger of the upper accumulator, valved connections extending from the heat exchanger of the upper accumulator to the bubbler pipe and heat exchanger of the lower accumulator.

6. An accumulator system for relief material from a pressure digester comprising in combination a pressure digester, two accumulators, connections for establishing communication from one accumulator through the other to the digester for transfer of li not into the digester, a bubbler pipe and a eat exchanger in one accumulator, connections from the digester to said bubbler and said heat exchanger, 9. bubbler pipein the other accumulator, and a connection from the heat exchanger to said bubbler pipe.

7. An accumulator system for relief material from a pressure digester comprising in combination a pressure digester, two accumulators, connections for establishing communication from one accumulator through the other to the digester for transfer of li uor into the digester, a bubbler pipe and a eat exchanger in one accumulator, connections from the digester to said bubbler and said heat exchanger, a heat exchanger in the sec- 7 terial from a pressure digester comprising in combination a pressure digester, two accumulators, connections for establishing communication from one accumulator through the other to the digester for transfer of liquor into the digester, a heat exchanger in one accumulator, a connection from the digester to said heat exchanger, a bubbler pipe in the other accumulator and a connection from the heat exchanger to the bubbler pipe.

9. An accumulator system for relief material from a pressure digester comprising in combination a pressure digester, two accumulators, connections for establishing communication from one accumulator through the other to the digester for transfer of liquor into the digester, a heat exchanger in one accumulator, a connection from the digester to said heat exchanger, a bubbler' pipe and a heat exchanger in the other accumulator, and connections from the first named heat exchanger to the second named heat exchanger and to the bubbler pipe.

10. The method of treating cooking liquor for a sulphite-process of cooking wood and the like which comprises relieving a sulphite digester during its operation, dischargin the relief material under pressure into a con ed body of liquor, subsequently cutting off said discharge when the back pressure interferes with relief of the digester, continuing relief of the digester, using said subsequently formed relief material as a source of heat for a second body of confined liquor, and conducting one body of liquor into a digester as a cooking liquor, and treating the remaining bod of liquor in the manner in which the use body of liquor was treated.

. 11. The method of charging a digester with a highly charged acid sulphite liquor which comprises saturatin a confined volume of sulphite liquor un er pressure with sulphurous acid, in an accumulator tank, and moving said volume of liquor bodily from said tank into a digester by pressure from a replacing volume of liquor.

12. Apparatus for charging a digester with a highly char ed acid sulphite liquor comprising in combination'with a digester, an accumulator, means to heat liquor in 'said accumulator, means to charge sulphurous acid.

into said liquor in said accumulator under pressure, a connection from near the top of said accumulator leading to a digester, a connection entering the accumulator near the bottom thereof, and means to force fresh liquor under pressure into said accumulator through said bottom connection, whereby charged liquor in the accumulator may be forced bodily into said digester.

13. The method of charging a digester with a highly charged acid liquor which comprises saturating a confined volume of acid liquor under pressure with sulphurous acid in an accumulator tank, and moving said volume of llquor bodily from said tank into a .digester by pressure from a replacing volume of liquor arranged at a higher elevation than the second mentioned liquor.

In testimony whereof I have hereunto affixed my signature.

WILLIAM H. KENETY. 

